1. Field of the Invention
The present invention relates to the electromechanical arts and energy storage systems. In particular, the present invention relates to flywheel systems used for energy storage and conversion.
2. Description of Related Art
Flywheel energy storage systems have provided a mechanical energy storage solution for hundreds of years as evidenced by the potter's wheel. Such systems differ in many respects from modern-day flywheel energy storage solutions. More recent design imperatives including high power density and electric power outputs have led to lightweight, high-speed flywheels operating in evacuated chambers and driving a similarly high-speed electric generator.
A typical application for today's flywheel is to provide electric power to an electric network for a brief period of time, as might be needed when an electric power outage occurs. Such applications require that the flywheel operate in a stand-by mode, fully charged and ready to convert its mechanical energy into electrical power to support the electrical network when network supply voltage droops.
To the extent that a protracted power outage occurs and the flywheel's usable electric output is depleted by the external electric network, the flywheel's internal electrical loads may be deprived of the electric power required to complete a normal flywheel shutdown. Critical loads internal to the flywheel system may include electric and electronic controls.
Supplying electric loads internal to the flywheel system during coast down presents a particular problem when the flywheel's electric generator has a minimum operating speed as is typical of inductive generators. Here, another source of electric power will be needed during some portion of the coast down period.